California’s faith-based experiment in combating climate change is heading straight for the wallets of gasoline consumers in 2015.

That’s when a “cap-and-trade” market system designed to limit greenhouse-gas emissions is scheduled to expand from big industrial companies into the state’s vast gasoline market. The idea is that a producer who cuts emissions can sell unneeded credits to other companies for a profit, creating incentives for more reductions.

Pump prices will probably edge up 12 cents a gallon in January, according to one reported estimate, but nobody knows how much the system ultimately will cost.

Such uncertainty appears to have the Democrats who run state government worried about presiding over an Obamacare-like rollout or, even worse, the kind of market dysfunction we saw in 2000 and 2001, when flawed legislation produced California’s power crisis.

How worried are they? Last week, state Senate leader Darrell Steinberg, D-Sacramento, proposed scrapping cap-and-trade and replacing it with a carbon tax.

You’re probably wondering what’s so remarkable about a Democrat calling for a new tax. But in theory this isn’t just any tax; it’s what’s known as a “Pigovian” tax, and it falls into that rare category of policies that both liberal and free-market economists tend to agree upon.

In the early 20th century, British economist Arthur Cecil Pigou observed that some activities cause “externalities,” or costs, for neighbors and society at large without compensating them for their trouble. He used the example of a game preserve that caused a neighbor’s land to be overrun with rabbits.

If the neighbors couldn’t agree on compensation, Pigou’s solution was for government to tax the offending activity, thus raising the cost and leading to less of it. And ideally, any revenues would be used to repair the consequences.

For a potent example of this concept at work, consider the steep tax hikes on tobacco of recent years, which have caused big reductions in smoking and cut overall health care costs.

Pollution is another classic example, because markets typically fail to deliver prices that reflect the true costs of environmental damage.

Scientists have argued for a few decades that greenhouse gases are causing rapid global warming and should be classified as pollutants, particularly if they are produced by burning fossil fuels.

In 1997, an open letter co-written by liberal economist Paul Krugman and signed by about 2,500 economists of every stripe called for governments to adopt a market-based strategy for cutting emissions, including a carbon tax.

The letter also made an important point: Governments could reduce the economic harm that inevitably flows from tax hikes by making carbon levies “revenue neutral,” or offset by reductions in other taxes.

More recently, Harvard economist Greg Mankiw, a conservative who advised former President George W. Bush, has proposed using escalating carbon taxes to fund Social Security. Then we could cut or eliminate payroll taxes, which discourage employment — something society wants more of.

However, economists also generally agree that properly designed cap-and-trade systems can work, too. Indeed, a market for pollution credits dramatically cut emissions of sulfur dioxide and nearly eliminated acid rain in the eastern U.S.